Do you need a visa for travel to Spain for one year from the USA?

Yes.

As a US citizen (and all other non-EU/EEA citizens), you are only allowed to stay in Schengen countries for up to 90 days as a tourist, and you are not allowed to work.

After 90 days (or if you want to work) you need a visa or work permit from the Spanish authorities.

If you are a citizen of an EU country, you have an automatic right to travel, live and work in Spain (and all other EU countries).